Bulk granular, particulate or powered materials are conveniently transported in containers or tankers which can be carried by road, sea or rail. Owing to the fluid nature of these materials they can be discharged from a container by the simple expedient of opening a container discharge outlet near the floor of one end of the container and raising the opposite end of the container to allow the material to flow out of the container discharge outlet under gravity. Unfortunately though, the rate at which material flows from the container under gravity is not easily controlled. Accordingly, it is common practice to connect a rotary valve seal to the discharge outlet of the container to assist in the discharge. By way of explanation, a rotary valve seal comprises a plurality of vanes equi-spaced about a rotatable axle to define a V-shaped vane compartment between each adjacent pair of vanes. This assembly is mounted in a housing which has a material inlet port at the top through which material can enter the uppermost vane compartment, and which has a compressed air inlet and a material discharge port at the bottom, positioned at opposite ends of the lowermost vane compartment. As the multi-vane assembly is rotated, it picks up material in the uppermost vane compartment by blowing it out through the material discharge port.
As indicated above, as the lowermost vane compartment passes between the compressed air inlet and the material discharge port, the material in the vane compartment is expelled under pressure. However, the vanes are moving relatively fast, and a volume of high pressure air will ussually remain in each vane compartment after it is emptied, together with a residual quantity of material. If this volume of high pressure air is allowed to reach the material inlet port, it will be vented into the container discharge outlet, causing a blowback of material into the shipping container and inhibiting the passage of material into the vane compartment. Accordingly, the vane compartment must be vented before it reaches the material inlet port. To this end, a venting port is provided in the side of the housing so that each vane compartment will pass the venting port before it passes the inlet port. To prevent any residual material in the vane compartment being expelled to atmosphere, a cloth filter is provided across the venting port mouth. Unfortunately, these cloth filters are prone to leakage in the initial period of their use and eventually become clogged.
Unless the connection between the container discharge outlet and the rotary valve seal material inlet port forms a tight seal, material may leak out. This is undesirable, particularly where the material being discharged is hazardous. Of course, it is always possible to use an elaborate coupling device between the container discharge outlet and the material inlet port which prevents leakage of material, but such coupling devices are complex in construction and cannot readily be transferred from one shipping container to another. Moreover, the coupling device must be able to accommodate changes in the relative positions of the container discharge outlet and the rotary valve seal inlet port as the container is tipped to bring material toward its discharge outlet.
In order to prevent material contaminating the interior of the shipping container, making it necessary to clean the container out after each new load, it is known to provide a polyethylene liner inside the shipping container. The liner comprises a plurality of filling sleeves in the top through which the liner can be filled and a discharge sleeve at the bottom through which the liner can be emptied.